Charged particle radiation measuring method and charged particle radiation measuring device

ABSTRACT

[Problem] To provide highly heat-resistant and radiation-resistant radiation measuring equipment. 
     [Solution] Provided are a charged particle radiation measuring method and a charged particle radiation measuring device using a scintillator comprising a phosphor in which the main component is a SiAlON phosphor.

TECHNICAL FIELD

The present invention relates to a charged particle radiation measuringmethod and a charged particle radiation measuring device.

BACKGROUND ART

Advanced medicine using radiation-generating devices, such asheavy-particle therapy devices, and fundamental testing at acceleratorfacilities associated therewith require the precise and continuousmeasurement of the radiation doses and energies of charged particlesunder high radiation density conditions. In addition thereto, in theevent of accidents at nuclear power facilities such as nuclear powerplants or the like that make use of nuclear fission, as well as in thereactor environments inside nuclear fusion reactors, the development ofwhich has progressed in recent years, radiation measuring equipment mustbe installed in high-temperature, high-environmental-load andhigh-radiation environments in order to take measurements.

The ion beams generated by accelerator facilities and the radiation fromnuclear power facilities is generally of high density, and in chargedparticle-irradiated environments in which the surrounding environment isalso at a high temperature, most radiation measuring equipment must behighly reliable.

When taking such measurements, scintillation-type detectors usingscintillators are used, and the durability and luminous efficiency ofthe luminescent material parts that convert radiation to light areextremely important. Scintillators are substances that generate lightwhen radiation impinges thereon, and they are used in positron emissiontomography (PET) devices and in industrial applications as well as inthe aforementioned radiation measurement applications and in acceleratorfacilities such as those used in heavy-particle therapy. In currentα-ray measuring equipment, materials such as ZnS:Ag,Cu and the like arewidely used for the luminous efficiency thereof (see Patent Document 1,Patent Document 2 or Non-Patent Document 1).

However, the scintillator materials such as ZnS:Ag,Cu that are currentlyused are not recommended for use at a temperature range of approximately100° C. or higher. For this reason, the properties of the materials arenot suitable for radiation measurement in nuclear power facilities, forwhich they would be expected to be used in high-temperatureenvironments.

Moreover, ZnS:Ag,Cu and the like have the problem that the luminousintensities thereof are significantly degraded by high-densityradiation, and thus, they require frequent replacement.

RELATED ART DOCUMENTS Patent Documents

-   Patent Document 1: JP 2007-70496 A-   Patent Document 2: JP 2010-127862 A

Non-Patent Documents

-   Non-Patent Document 1: Transactions of the Materials Research    Society of Japan, Vol. 38, No. 3, 2013, pp. 443-446.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The degradation caused by radiation at nuclear power facilitiesadversely affects the dose measurements of said radiation, and poses aproblem for reliability. Additionally, high-density charged particleirradiation is also to be expected in accelerator facilities and inmedical installations such as heavy-particle therapy facilities makinguse thereof. There are still problems that need to be addressed inradiation measuring equipment making use of existing scintillators, suchas the problem of ensuring high performance in the beam quality of suchequipment and in that the decrease in work efficiency due to replacementprocedures significantly inhibits the operating efficiency ofaccelerator devices.

With the existing scintillator materials (ZnS:Ag,Cu) that are widelyused in conventional scintillator-type charged particle (α-ray)detectors, prolonged installment in high-temperature environmentsexceeding one hundred and a few tens of degrees (° C.) resulted inproblems such as not being able to precisely measure the doses of thecharged particles over long periods of time, and even for the measureddoses, not being able to take precise measurements thereof.

Meanwhile, in beam monitor measurement applications for charged particlebeams generated by accelerator facilities or the like, high-density ioncurrents are to be expected. With existing scintillator materials(ZnS:Ag,Cu), there is significant attenuation in the light output, andreplacement becomes necessary, for example, when the cumulative numberof ions exceeds 10¹⁵ per square cm (hereinafter expressed as 10¹⁵[ions/cm²]). Additionally, even for measurements before that number isreached, it is necessary to account for the degradation in the luminousefficiency in order to determine the radiation dose from the lightoutput, so precise measurements cannot be made.

These problems are relevant to the fields of fundamental and appliedphysics relating to radiation measuring equipment for measuring α-raysin nuclear power facilities, advanced medical device installationsmaking use of radiation generating devices such as heavy-particletherapy devices, and other accelerator facilities associated with theuse of charged particles, as well as to the field of industrialequipment having compact accelerator mechanisms such as ion implantationdevices.

The present invention was made in consideration of the above-describedbackground, and has the purpose of providing highly heat-resistant andradiation-resistant radiation measuring equipment.

Means for Solving the Problems

The present invention provides a charged particle radiation measuringmethod using a scintillator comprising a phosphor in which the maincomponent is a SiAlON phosphor.

The present invention provides a charged particle radiation measuringdevice comprising a scintillator comprising a phosphor in which the maincomponent is a SiAlON phosphor; an optical component that selectivelycollects light from the scintillator; and a measuring portion that readsout light induced by radiation.

In one embodiment of the present invention, the above-mentioned SiAlONphosphor is a phosphor in which the main component is a β-type SiAlONrepresented by the general formula: Eu_(x)Si_(6−z)Al_(z)O_(z)N_(8−z),where 0.01≤x≤0.5 and 0<z≤4.2, and having an Eu luminescence center.

In one embodiment of the present invention, the above-mentioned SiAlONphosphor is a phosphor in which the main component is an α-type SiAlONrepresented by the general formula:M_(y)Si_(12−(m+n))Al_((m+n))O_(n)N_(16−n), where M includes at least oneelement chosen from among Li, Ca, Mg, Y and lanthanides, with theexception of La and Ce, and at least one luminescence center chosen fromamong Eu, Ce, Tb, Yb, Sm, Dy, Er and Pr, where y=m/p, in which p is thevalence of M, and where 0.3<m<4.5 and 0≤n<2.5.

Effects of the Invention

According to the present invention, highly heat-resistant andradiation-resistant radiation measuring equipment can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a radiation dose measuringdevice according to one embodiment of the present invention.

FIG. 2 is an example of beam measurement in a radiation dose measuringdevice according to an example.

FIG. 3 is an example of wavelength measurement in a radiation dosemeasuring device according to an example.

FIG. 4 is an example wherein the radiation resistance of a radiationdose measuring device was tested by means of high-density radiation.

MODES FOR CARRYING OUT THE INVENTION

Hereinbelow, embodiments of the charged particle radiation measuringmethod and the charged particle radiation measuring device according tothe present invention will be explained with reference to the attacheddrawings. However, it should be clear that the present invention is notlimited to these embodiments.

The charged particle radiation measuring method and the charged particleradiation measuring device according to the present embodiment use, asscintillator materials, phosphors in which the main component is aSiAlON phosphor.

SiAlON phosphors are representative oxynitride phosphors. They arephosphors having luminescence centers that are activated by using, asthe host crystal, SiAlON, which was developed as an engineering ceramicthat maintains good mechanical properties at high temperatures. Thereare two types that differ in their crystal structures.

β-type SiAlON is a green-emitting phosphor represented by the generalformula: Eu_(x)Si_(6−z)Al_(z)O_(z)N_(8−z), where 0.01≤x≤0.5 and 0<z≤4.2,and having an Eu luminescence center.

α-type SiAlON is a phosphor represented by the general formula:M_(y)Si_(12(m+n))Al_((m+n))O_(n)N_(16-n), where M includes at least oneelement chosen from among Li, Ca, Mg, Y and lanthanides, with theexception of La and Ce, and at least one luminescence center chosen fromamong Eu, Ce, Tb, Yb, Sm, Dy, Er and Pr, where y=m/p, in which p is thevalence of M, and where 0.3<m<4.5 and 0≤n<2.5.

It is known that when these SiAlON phosphors are used as phosphors inwhite LED devices in which luminescence occurs by excitation with bluelight from a blue LED chip, the luminescence intensity is not reduced bymuch even if the environmental temperature rises to 300° C., anddegradation is not observed even when the phosphors are left in ahigh-temperature, humidity-resistant (85° C., 85% relative humidity)environment.

The present inventors discovered that SiAlON phosphors have extremelylow susceptibility to degradation in high-temperature environments andby irradiation with high-density radiation compared with existingscintillator materials such as ZnS:Ag,Cu phosphors and the like.

In the radiation measuring equipment according to the presentembodiment, the luminescence spectrum of light induced by radiation inthe highly heat-resistant and radiation-resistant SiAlON phosphor ispreferably adjusted so that the peak wavelength is a wavelength at whicha light sensor has high quantum efficiency.

The charged particle radiation measuring device according to the presentembodiment comprises a scintillator comprising a phosphor in which themain component is a SiAlON phosphor; an optical component thatselectively collects light from the scintillator; and a measuringportion that reads out light induced by radiation.

The radiation measuring equipment according to the present embodimentmay be formed by combining a mechanical component, such as a holder thatholds and fixes the SiAlON phosphor, in a form such as a powder, asintered compact, a single crystal or a thin film; an optical componentthat selectively collects the radiation-induced light from thescintillator; and a measuring portion, such as camera equipment, anavalanche photodiode (APD), a photomultiplier tube (PMT), a CCD elementor a photodiode (PD), that reads the photons induced by primaryradiation.

FIG. 1 is an example of a schematic structural diagram showing radiationmeasuring equipment. The radiation from an accelerator facility is usedas the primary radiation.

The emission wavelength can be adjusted by changing the composition ofthe SiAlON phosphor constituting the scintillator, thereby improving thereadout efficiency in the measuring equipment.

For α-rays in environmental radiation or the like, the radiation sourceis not a single point, but rather arrives from all directions so as tosurround the scintillator material. The scintillator material and themechanical component, optical component and measuring portion associatedtherewith may be configured in the same manner as that shown in FIG. 1.Additionally, since the mechanical component, the optical component andthe measuring portion must have a geometric structure and arrangementthat are suitable for the measurement target, the structures thereof maytake various forms depending on the purpose. By using one-dimensional ortwo-dimensional measuring equipment in the measuring portion, the modeof observation may be changed.

According to the present invention, charged particle measurements can bemade in high-temperature, high-load environments, even for measuringradiation from radiation sources other than radiation generatingdevices, using basically the same structural elements, though thestructure of the radiation measuring equipment will differ.

Although the heat-resistance performance of the components used in themeasuring equipment could raise problems, structural changes cannotoccur in the SiAlON phosphor even at high temperatures. Thus, bycombining the SiAlON phosphor with structural materials as well as anoptical component and a measuring portion that are appropriate, it ispossible to improve the operating temperature range of the radiationmeasuring equipment, which has higher radiation resistance thanconventional devices. As a result thereof, it is possible to prolong thelife spans of α-ray measuring equipment having the purpose of performingnormal radioactive contamination tests, and to realize and provideradiation measuring equipment for measuring α-rays inside nuclear powerfacilities or the like, where high-temperature resistance is required.

The charged particle radiation measuring method and the charged particleradiation measuring device according to the present embodiment may beused as a) radiation measuring equipment for measuring α-rays, used innuclear power facilities, that take measurements by means ofscintillation; b) beam monitors and radiation meters that are used formeasuring beam quality in radiation generating devices (accelerators) inheavy-particle or cation therapy devices; or c) beam quality measuringdevices or the like in other accelerator facilities that are associatedwith the use of charged particles, or in industrial equipment havingcompact accelerator mechanisms such as industrial ion implantationdevices.

In the charged particle radiation measuring device according to thepresent embodiment, by using a phosphor in which the main component is aSiAlON phosphor as a novel scintillator material, which is aradiation/light conversion material, it is possible to provide a highlyheat-resistant and radiation-resistant radiation measuring device thatcomprises the scintillator material, a mechanical component that holdsand fixes the scintillator material and an optical component thatselectively collects light from the scintillator, and a measuringportion that reads out radiation-induced light.

As described above, due to the charged particle radiation measuringmethod and the charged particle radiation measuring device according tothe present embodiment, it is possible to provide a radiation meter thatcan measure charged particle radiation doses regardless of theenvironment, and that can be used for a longer life span thanconventional devices, even under conditions in which the temperature isin the hundreds of degrees (° C.) or at high radiation doses such as infocused charged particle irradiated environments in which it wasconventionally difficult to use charged particle radiation meters.

EXAMPLES

Hereinbelow, examples of the present invention will be described.

Example 1

A β-type SiAlON:Eu powder (manufactured by Denka, GR-200 grade, β-typeSiAlON, average particle size: 21 μm) was dispersed in water glass, thencoated onto and evenly fixed to a carbon plate, to a coating filmthickness of 10 μm or less, to produce a scintillator. This scintillatorwas mounted on radiation measuring equipment as shown in FIG. 1, and acharged particle irradiation test was performed thereon.

From an adjacent accelerator facility, a 3 MeV H⁺ (proton) focused ionbeam was directed so as to continuously irradiate a localized (400μm×400 μm) target.

With the radiation measuring equipment of the present invention, it ispossible to measure the distribution and intensity of the primaryradiation by means of the spatial distribution or wavelengthdistribution of light. FIG. 2 shows an example of beam measurement usingthe radiation measuring equipment. FIG. 3 shows the results ofmeasurement of the spectrum and luminescence intensity of lightgenerated by excitation by charged particles.

Example 2

Using an α-type SiAlON:Eu powder (manufactured by Denka, YL-600A grade,α-type SiAlON, average particle size: 15 μm), a scintillator wasproduced using the same method as that in Example 1, and a chargedparticle irradiation test was performed thereon.

Comparative Example 1

As Comparative Example 1, charged particle irradiation tests wereperformed under the same conditions as those in Example 1, but using aZnS:Ag phosphor powder instead of the above-mentioned α-type SiAlON:Eupowder.

FIG. 3 shows measurement results for the spectra and luminescenceintensities of Examples 1 and 2 and Comparative Example 1 at the time ofcommencement of the tests. When exposed to the same radiation dose, atthe time of commencement of the tests, charged-particle-excitedluminescence of about the same luminescence intensity as that inComparative Example 1 using ZnS:Ag was observed, at slightly longerwavelengths, in Example 1 using the α-type SiAlON:Eu phosphor. Theluminescence wavelength of the β-type SiAlON:Eu phosphor was morefavorable in that the quantum efficiency of the optical sensor washigher at that wavelength as compared to the luminescence wavelength ofZnS:Ag.

Additionally, in Example 2 using α-type SiAlON, charged-particle-excitedluminescence was observed at longer wavelengths than in β-type SiAlON.The luminescence intensity for α-type SiAlON was lower than that forβ-type SiAlON, but about the same value was obtained when integratingthe luminescence intensity over the luminescence spectrum.

FIG. 4 shows the results of high-density irradiation tests of radiationmeasuring equipment using Examples 1 and 2, and Comparative Example 1.The charged particle doses are indicated on the horizontal axis and theluminescence intensities at the same radiation intensities are shown onthe vertical axis.

It can be seen that, as the charged particle dose increases, theluminescence intensity of Comparative Example 1, which uses ZnS:Ag,attenuates significantly. In contrast thereto, in the case of Example 1,which uses a β-type SiAlON:Eu phosphor, attenuation of the luminescenceintensity is not observed, and it can be confirmed that the fluorescenceproperties are not degraded by high-density radiation. In Example 2,which uses an α-type SiAlON:Eu phosphor, attenuation of the luminescenceintensity was observed, but it can be seen that the attenuation wassmall in comparison to Comparative Example 1, which uses ZnS:Ag.

From the above results, it can be understood that the charged particleradiation measuring method using a SiAlON phosphor according to thepresent invention is fully capable of being used in a highlyheat-resistant and radiation-resistant radiation meter. As a resultthereof, measurements of radiation intensity and dose based onluminescence intensity can be made for a long period of time by usingthe output from the measuring portion of the radiation meter, whichutilizes a SiAlON phosphor.

Furthermore, as shown in FIG. 2, it is possible to measure a beam spotin two dimensions, and to measure the distribution of the primaryradiation.

In the present example, the radiation source is radiation from anaccelerator facility, so the test is a highly accelerated test in whichthe measurement time is only about a few hours. However, for α-rays inenvironmental radiation or the like, such numbers mean that the devicewould be highly resistant even to degradation on the order of years.Additionally, since the fluorescence properties of SiAlON are maintainedeven under conditions in which charged particles are continually heatedin a localized area, the present invention can be used even inhigh-temperature environments of hundreds of degrees (° C.).

The invention claimed is:
 1. A charged particle radiation measuringmethod utilizing a scintillator comprising a phosphor in which the maincomponent is a SiAlON phosphor, wherein the SiAlON phosphor is aphosphor in which the main component is a β-type SiAlON represented bythe general formula: Eu_(x)Si_(6−z)Al_(z)O_(z)N_(8−z), where 0.01≤x≤0.5and 0<z≤4.2, and having an Eu luminescence center.
 2. A charged particleradiation measuring device comprising: a scintillator comprising aphosphor in which the main component is a SiAlON phosphor; an opticalcomponent that selectively collects light from the scintillator; and ameasuring portion that reads out light generated by radiation, whereinthe SiAlON phosphor is a phosphor in which the main component is aβ-type SiAlON represented by the general formula:Eu_(x)Si_(6−z)Al_(z)O_(z)N_(8−z), where 0.01≤x≤0.5 and 0<z≤4.2, andhaving an Eu luminescence center.